Thermal protective device



Sept. 12, 1933. G. LONG THERMAL PROTECTIVE DEVICE Filed NOV. 7, 1930 Patented Sept. 12, 1933 UNITED STATES PATENT OFFICE 13 Claims.

The present invention relates in general to thermal protective devices adapted to be made responsive to a fixed or given temperature and to actuate a signal or alarm, or to throw into or out of operation various devices, when the predetermined temperature has been reached or exceeded. More particularly, the present invention is principally concerned with the provision of a detachable fuse link for use in such devices and which is provided with a fusible element which can be easily and quickly attached or removed. 'In thermal protective devices of the usual type there is included a pair of biased members maintained or held in biased relationship by means of connections including a fusible member. When the predetermined temperature is reached or exceeded', the fusible member melts or collapses thereby releasing the biased members and permitting relative movement therebetween. This movement is made use of in actuating the signal or alarm, or throwing into or out of operation various other devices. After the biased members have been released and it is desired to again put *the thermal'protective device in operation it is necessary that the fusible member be replaced. The chief advantage, therefore, of the provision of a detachable fuse link which can be quickly attached or removed is that a thermal protective device is provided which can quickly and conve'niently be restored to operating position after having been tripped or operated.

In this respect, the present invention contemplates the provision of arelatively short detachable connecting rod or link which carries the fusible element and which is adapted to be received in a slot in one of the biased members so that the fuse rod or link can be removed and replaced by simply moving it into and out of the slot in the said biased member.

The present invention also contemplates other features of importance in the art of thermal protective devices. For example, another object of the present invention is to make use of a fuse link having a shoulder or groove to receive a fusible ring. When the predetermined temperature is reached or exceeded the stem shears material from the inner portion of the fusible ring due to the factv that the excessive temperature fuses or makes soft the fusible ring itself. By arranging the stem to shear material from the inner portion of the fusible ring when the same 1 is plastic due to high temperature an important portion thereof from radiant or reflected heat which might be reflected from the walls of the vessel or furnace in which the thermal protective device is situated. Thus the fusible link structure is responsive only to the temperature of the gases in the vessel or furnace.

Another feature of importance of the present invention is the use of relatively pure metal for the material of the fusible ring, and this is for the purpose of securing a fusible material having a short plastic range. The chief and most important result from using such material is that the thermal protective device is made more sensitive and positive in its operation.

Other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description of the preferred structural embodiment, illustrated in the accompanying drawing, in which:

Figure 1 is a plan view of my improved thermal protective device;

Figure 2 is a view taken at right angles to Figure 1;

Figure 3 is an enlarged fragmentary detail showing the inner ends of the biased members and the connecting fusible element;

Figure 4 is a sectional view taken substantially along the line 44 of Figure 3; and

Figure 5 is an enlarged view showing the grooved stem and the fusible ring or collar fixed thereto.

For the purpose of illustrating the present invention I have chosen a' thermal protective device embodying a tubular member in the form of a housing or mounting member 1 having at its outer end screw threads 2 for the reception of a switch housing 3, the latter comprising insulated contacts 4 and 5 of the usual type. Leads '7 and 8 are electrically connected, respectively, with the contacts 4 and 5 and are extended to some form of signal or alarm, or operating devices (not shown) The inner end of the mounting member or casing 1 is provided with va web or bridging portion 10 having a slot 11 therein for a purpose to be described later. Preferably the slotted web 10 is formed to provide openings 12 on either side thereof.

A member or rod 15 extends longitudinallywithin the tubular housing or casing 1 and at its outer end the rod 15 is provided with a contact or blade 17 (Figure 1) preferably insulated from the rod 15 and which is adapted on relative movement of the members 1 and 15 to close an electric circuit by connecting the contacts 4 and 5.

A spring 19 is interposed between the outer end of the rod member and the bottom of the switch housing 3 for the purpose of biasing the rod 15 for outward movement relative to the housing member or casing 1. The inner end of the rod 15 is formed with a hook portion or loop 21 which is arranged to lie between the two openings 12 when the spring 19 is compressed. A fuse link 24 is also provided with a loop or hook portion 25 adapted for hooked engagement with the rod 15. The fuse link 24 also has a stem 27 adapted to extend through the slot 11.

Relative movement between the member 1 and the biased member comprising the rod 15 and the link 24 is prevented by virtue of a fusible ring or collar 30 which is fixed to the stem of the fusible link 24 and is adapted to bear against the innermost wall or surface of the web 10 on the member 1. A groove 31 is provided near the end of the stem 27 and preferably this groove is arcuate or curved in cross section so as to snugly receive the inner surface or portion of the fusible ring 30. This ring may be applied to stem 27 in any suitable manner. It may be a split ring, or it may be merely a suitable length of fusible material, the ends of which are twisted together for securing the ring in groove 31. As best shown in Figure 3, the width of the slot 11 is only slightly greater than the diameter of the stem 27 so that the fusible ring 30 is firmly seated against the web 10 by the action of the spring 19. In this way, therefore, members 1 and 15 are biased for relative movement, which movement is prevented by the fuse link 24 and the fusible ring or coller 30. The material of the ring or collar 30 is such that it will fuse or become plastic at a temperature to which the thermal protective device is to be made responsive. As a matter of practice, I prefer to form the fusible element 30 of relatively pure metal for the reason that pure metals have a short plastic range. When employing fusible elements of such material there is little likelihood that the element will become soft and release the biased members until the given or predetermined temperature is actually.

reached. More specifically, I have found that the rings 30 may be made of gold if that metal fuses at the temperature to which it is desired that the thermal protective device should respond. This particular metal has the advantage of having a relatively short plastic range and the further advantage of not oxidizing at high temperatures. Preferably the members 1 and 15 and the fuse links '24 are made of nicrome, a material which will withstand high temperatures. The use of gold in the fusible element has the further advantage when used'with nicrome members of not amalgamating with the nickel or absorbing the same from the nicrome members. It is, of course, to be understood that under other conditions the fusible element may be made of metals of the binary or trinary systems or other alloys, and such is to be contemplated as within the scope of the present invention. It is also to be understood that where the thermal protective device is used in high acid atmospheres the device may be covered by a housing of refractory material if found desirable or necessary.

Referring now to Figure 5, it will be observed that the groove 31 is relatively shallow and that the innermost portions only of the fusible element 30 are received therein. This figure shows clearly that the fusible element 30 seats firmly against the web 10 all around the stem 27 and that the wall 31a bears against the inner surface of the ring 30. It is also to be noted that the groove 31 embraces the inner surface or portion of the ring 30 to the extent corresponding to an are or segment of only degrees. The arrow 35 in Figure 5 indicates the direction of stress relative to the web 10 occasioned by the biasing spring 19, and it will therefore be clear that when the fusible ring 30 becomes plastic the wall 31a of the groove 31 will shear a small amount of material from the inner portion of the ring 30, thereby releasing members 1 and 15 and allowing the blade 17 to connect the contacts 4 and 5, actuating any form of signal, alarm or device may be desired.

The feature of releasing the biased members by shearing a portion from the inside of the ring when the latter is plastic secures a number of advantages. In the first place, it will be noted that the zone of shear, which is represented by the dotted lines 37 in Figure 5 and is actually a cylinder, is in such a position relative to the cross section of the fusible ring 30 that it is removed from and protected against any reflected or radiant heat in the proximity of the inner 0nd of the thermal protective device. That is, the outer portion of the fusible ring 30 serves to protect the inner portion and hence the zone of shear 37 is also shielded and protected.

The openings 12 in the inner end of the mounting or casing member 1 are such that, together with the slot 11 in the bridging or connecting 10, it is an easy matter to insert a new fuse "4 when the fusible element on the preceding link 24 has been fused and the biased members thereby released. All that is necessary to do is to grasp the outer end 17 of the rod 15 and for- 'cibly move the same against the action of the and the parts will be held in biased relationship until the element 30 is fused or becomes ,plaaic which time, as will be understood and 88 6,!- plained above, the stem 27 shears the inner surface of the element 30 and releases the member 15 to actuate the signal or the devices associated with the contacts 4 and 5. The link 24 is short and may be replaced at small cost and with facility, which is advantageous as avoiding any necessity for replacing rod 15 and associated parts, with attendant relatively great cost and considerable loss of time. It is to be understood, of course, that the contacts 4 and 5 can be arranged to break or open a circuit rather than complete a circuit as indicated in Figure 1. Furthermore, it is within the scope of the present invention to associate one or more relays or other devices with the contacts 4 and 5 so as to actuate a device or devices for actuating one or more controls if and when desirable. When the thermal protective device of the present invention is to be employed in a furnace, obviously the members 1 and 15 can be of any desired length sufficient to pass through the walls of the furnace and to place the inner end bearing the fuse link 24 in thermal relationship with the interior of the furnace. It is, of course, obvious that the present invention is not limited to use with a furnace but can be used in many different installations, the only essential being that the material of which the fusible element 30 is formed shall be fusible at the desired temperature.

While I have shown and described the preferred structural embodiment of the present invention it is to be understood that my invention is not tobe limited to the specific structure shown and described but that, infact, widely different means may be employed in the practice of the broader aspects of, myinvention.

What I claim, therefore, and desire to secure by Letters Patent is: I v

1. A thermal protective device comprising a mounting, an indented member movably supported in said mounting and biased toward one position therein, a fusible ring fixed to and surrounding said member and having a portion thereof confined within the indentations of said member, said ring bearing against said mounting for holding the member against movement in the direction in which it is biased until a predetermined temperature is reached when the member is released by the fusing of the ring.

2. A thermal protective device comprising a mounting member, a movable member movably supported in biased relationship with respect to the mounting member, a detachable link having hooked engagement with one of said members,

the other of said members having an open ended slot for receiving said link and permitting its attachment and removal, and a fusible ring securely fixed to said link and adapted to bear against the walls adjacent the slotted portion of said other member and to prevent movement of said one member and the connected link relative to said other member until a predetermined temperature is reached.

3. A thermal protective device comprising a mounting member, a movable member movably supported in biased relationship with respect to the mounting member, a detachable link having hooked engagement with one of said members, the other of said members having an open ended slot for receiving said link and permitting its attachment and removal, a fusible ring securely fixed to said link and adapted to bear against the walls adjacent the slotted portion of said other member and to prevent movement of said one member and the connected link relative to said other member until a predetermined temperature is reached, and an electric switch means adapted to be actuated by said relative movement.

4. A thermal protective device for use at high temperatures comprising a mounting of nicrome metal and tubular in formation, a rod of nicrome metal movably held in said mounting, means biasing said rod for movement in one direction in the mounting, and a fuse link connected with the rod and the mounting for holding the rod against movement in said direction until a predetermined temperature is exceeded, said fuse link comprising a member formed of nicrome and provided with a circumferential groove, a circular fusible member formed of material having a short plastic range and seated in the groove, said member bearing against the mounting.

5. A fusible link for thermal protective devices adapted to hold a pair of members in biased relationship and to release said members when a predetermined temperature is exceeded, said link comprising a connection having an annular groove associated with one member and a toroidal fuse ring associated with the other member and seated in the groove in said connection.

6. A fusible link for thermal protective devices adapted to hold a pair of members in biased relationship and to release said members when a predetermined temperature is exceeded, said link comprising a hook member connected to one of said first named members and provided with a stem having circumferential groove, and a fusible collar partly seated in the groove and connected with the other of said first named members,

whereby when said predetermined temperature is exceeded the collar becomes plastic and said first named members are released.

'7. A fusible link for thermal protective devices adapted to hold a pair of members in biased relationship and to release said members when a pre determined temperature is exceeded, said link comprising a hook member connected to one of said first named members and provided with a stem having circumferential groove arcuate in cross section, a fusible ring having a cross section corresponding to that of said groove and seated in the latter to an extent corresponding to an are along the circular cross section of the ring of approximately said fusible ring being adapted to be seated against the other of said pair of members, whereby when said predetermined temperature is exceeded the ring becomes plastic and the walls of the groove shear the ring material therein from the remaining material of the ring to release said pair of members.

8. A fusible link for thermal protective devices adapted to hold a pair of members in biased relationship and to release said members when a predetermined temperature is exceeded, said link comprising a hook member connected to one of said first named members and provided with a stem having circumferential groove arcuate in cross section, a toroidal fusible member having a circular cross section and partly seated in said groove, said fusible member being dimensioned to extend outside the circumference of said stem and adapted to bear against the other of said pair of members so that when said predetermined temperature is exceeded said pair of members are released.

9. As an article of manufacture, a fuse link for a thermal protective device, said linking comprising a loop and a stem extending therefrom, said stem being formed with a groove, and a fusible collar fixed in said groove.

- 10. As an article of manufacture, a fuse link for a thermal protective device or the like, said link comprising a body having a loop at one end and adapted for detachable connection in said device and a stem at the other end, said stem being provided with a shoulder, and a fusible element surrounding the stem and seated against said shoulder.

11. A fusible link for thermal protective devices adapted to hold a pair of members in biased relationship and to release said members when a predetermined temperature is exceeded, said link comprising means forming a shallow shouldered groove associated with one of the biased members and extending in closely spaced relationship with respect to the other member, and a fusible ring having its inner portion seated in the groove and protected from radiant heat by the outer portion of the ring, said ring being seated against said other member.

12. A fusible link for thermal protective devices adapted to hold a pair of members in biased relationship and to release said members when a predetermined temperature is exceeded, said link groove associated with one of the biased members and extending in closely spaced relationship with respect to the other member, and a fusible ring having its outer portion bearing against the other of said biased members and having its in comprising means forming a shallow shouldered" her, and fusible means co-operating with the stem of the link and said member for normally holding said link against movement toward said other end oithecasingthelinkandtherodhavinglntfiengaginghookandloopelementsandthecadnz having an opening disposed to permit insertion of the stem of the link through said member and interengaging of the hook and loop elements at the link and the rod, in substantially normal position of the latter.

GEORGE LONG. 

